DRILLING KICK-OFF DEVICE

Abstract: Kick-off device (1) in aid of drilling a pair of opposite deviated borehole branches in an underground formation from a single borehole comprising an open-ended tube (2) provided at its upper end with connecting means to join the open-ended tube (2) to a string of casing, and a guide element (4) arranged in the open-ended tube (2) near its lower end, which guide element (4) includes two hollow slanted guide ways (6 and 7) arranged on opposite sides of the guide element (4), wherein the wall of the open-ended tube (2) has elongated openings (9 and 10) facing the slanted guide ways (6 and 7).

Description: DRILLING KICK-OFF DEVICE The present invention relates to drilling deviated borehole branches in an underground formation from a single borehole. The single borehole is in general a vertical borehole and in order to reach widely spread targets one or more deviated borehole branches are drilled from the single borehole. In one way of drilling a deviated well use is made of a kick- off device in the form of a steel weripe or whipstock arranged on the bottom of the single well. On continuing drilling, the drill bit follows the wedge and a deviated borehole branch is drilled. After having drilled a short length of the deviated borehole branch, the whipstock is removed and drilling in the deviated branch is continued. See for a description of this method The Petroleum Handbook, 6th Edition, Elsevier, 1983, pages 135-136. When it is required to drill two of opposite borehole branches the second borehole branch can be drilled using a whipstock orient¬ ed in a direction opposite to the direction of the first borehole branch. A kick-off device used to drill more than one deviated borehole branch is disclosed in USA patent specification No. 4 573 541. This device comprises a tubular housing and three guide tubes arranged in the housing of which two are curved away from the central longitudinal axis of the housing. Drilling a deviated borehole branch comprises arranging the device in the lower end of the cased single borehole, guiding the drill bit into one of the two curved guide tubes and continue drilling. A disadvantage of this kick-off device is that the diameter of the guide tubes is smaller than half the diameter of housing and consequently the curved borehole branches have a diameter which is much smaller than the diameter of the original borehole from which they are drilled- It is an object of the present invention to provide a kick-off device that allows drilling a pair of opposite deviated borehole branches, wherein the maximum diameter of the branched borehole section is limited by the diameter of the drill bit that can pass through the cased single borehole. To this end the kick-off device in aid of drilling a pair of opposite deviated borehole branches in an underground formation from a single borehole according to the present invention comprises an open-ended tube provided at its upper end with connecting means to join the open-ended tube to a string of casing, and a guide element arranged in the open-ended tube near its lower end, which guide element includes two slanted guide ways arranged on opposite sides of the guide element. Suitably the slanted guide ways are hollow. To avoid drilling through a metal wall, the wall of the open- ended tube has elongated openings facing the slanted guide ways. The open-ended tube may also be provided at its lower end with connecting means to join one or more additional joints of casing to the lower end of the open-ended tube in order to centralize the open-ended tube in the single borehole. The invention also relates to a re-entry device which can be removably placed in the kick-off device of the present invention, which re-entry device comprises an open-ended liner having an elongated opening in its wall, a slanted deflecting surface ar- ranged in the open-ended liner facing the elongated opening, wherein when the re-entry device can be so placed in the kick-off device that the slanted deflecting surface meets one of the two slanted guide ways. Suitably the re-entry device further comprises a meeting element arranged in the lower end part of the open-ended liner, which meeting element has a sole to allow the meeting element to rest on the guide element and includes a wedge-shaped part to allow placing the meeting element in a predetermined position with respect to one of the slanted guide ways. The invention will now be described by way of example in more detail with reference to the accompanying drawings, wherein Figure 1 shows schematically a side view of the kick-off device according to the present invention; Figure 2 shows a cross-sectional view along line II-II of Figure 1; Figure 3 shows a longitudinal view along line III-III of Figure 1; Figure 4 shows schematically and not to scale a pair of oppo- site deviated borehole branches drilled from a single borehole; Tigure 5 shows schematically a side view of a casing string provided with the kick-off device of the present invention; Figure 6 shows a partial cross-sectional view along line VI-VI of Figure 4; and Figure 7 shows schematically the kick-off device provided with a re-entry device according to the invention. Reference is now made to Figures 1 through 3. The kick-off device 1 of the present invention comprises an open-ended tube 2 provided at its upper end with connecting means (not shown) to join tne open-ended tube to a string of casing, and a guide element 4 arranged in the open-ended tube near its lower end 5. The guide element 4 includes two slanted guide ways 6 and 7 arranged on opposite sides of the guide element 4. In the embodi¬ ment shown the guide ways 6 and 7 are hollow. The wall of the open-ended tube 2 has elongated openings 9 and 10 facing the slanted guide ways 6 and 7. Reference is now made to Figures 4 through 6. Figure 4 shows schematically and not to scale the drilling of a pair of opposite deviated borehole branches 20 and 21 from a single borehole 22 drilled from a drilling rig 25 in an underground formation 27. The single borehole 22 has been cased with a casing string 28 which has been provided near its lower end with the kick-off device 1 accord¬ ing to the present invention. The casing string 28 is cemented in the single borehole 22 in a conventional way, the cementing opera- tion will not be discussed here. The lower end of the casing string 28 is shown in more detail in Figures 5 and 6. The kick-off device 1 is arranged between the last section 30 of the casing string and a tail section 31, to this end the open-ended tube 2 is provided at both ends with connecting means. The tail section 31 comprises a joint of casing and it serves to centralize the kick-off device 1 in the single borehole 22. The connections between the sections are referred to by reference numerals 32. The casing string 28 is furthermore provided with centralizers 33 to centralize the casing string 28 in the single borehole 22 (see Figure 4) . To drill a deviated borehole branch a drill string assembly 50 (see Figure 6) having a drill bit 52 at its lower end is lowered into the casing string 28. The guide element 4 deflects the drill bit 52 and on rotating the drill bit 52 drilling a deviated bore¬ hole branch is started. The hollow form of the guide ways 6 and 7 facilitates control of the direction of the drill bit 52 and the drill string assembly 50 as drilling continues. This is also shown in Figure 4, wherein the drill bit 52 is shown in the deviated borehole branch 21. In Figure 4 it has been assumed that branch 20 has already been drilled. To facilitate entering in one of the deviated borehole branch¬ es, a re-entry device can be lowered into the kick-off device of the invention, the outer diameter of the re-entry device being smaller than the inner diameter of the kick-off device. The re¬ entry device arranged in the kick-off device is shown in Figure 7. The re-entry device is referred to by reference numeral 60 and it has been removably placed in the kick-off device 1. The re-entry device 60 comprises an open-ended liner 61 having an elongated opening 62 in its wall, a slanted deflecting surface 64 arranged in the open-ended liner 61 facing the elongated opening 62. The re-entry device 60 has been so placed in the kick-off device 1 that the slanted deflecting surface 64 meets the slanted guide way 6 which is one of the two slanted guide ways 6 and . To orient the re-entry device 60, it further comprises a meeting element 66 arranged in the lower end part of the open-ended liner 61, which meeting element 66 has a sole 67 to allow the meeting element 66 to rest on the guide element 4 and includes a wedge-shaped part 68 to allow placing the meeting element 66 in a predetermined position with respect to one of the slanted guide ways 6 or 7. The re-entry device 60 is lowered into the casing string 28, for example at the end of a drill string (not shown) to which it is removably connected. After having placed the re-entry device 60 the drill string is pulled out of the borehole. When a tool has to be lowered into borehole branch 20 (see Figure 4) , the re-entry device 60 is placed in the kick-off device 1 as shown in Figure 7. The tool (not shown) is then lowered through the casing section and is guided along the slanted deflect¬ ing surface 64 into the borehole branch. To secure the re-entry device 60 in the kick-off device 1, the re-entry device 60 may include a releasable lock assembly (not shown) . The re-entry device 60 can also be used to drill one of the deviated borehole branches. To this end drilling the deviated borehole branch is started as described with reference to Figures 4-6. When about 1 has been drilled, the drill string assembly is removed from the borehole, the re-entry device is attached to the kick-off device and drilling the deviated borehole branch is resumed. To facilitate initial drilling of one of the deviated borehole branches a directional drilling assembly including a downhole motor and a bent-sub can be applied. With the directional drilling assembly selectively oriented the bent-sub forces the drill bit driven by the downhole motor through a selected one of the elongate openings of the open-ended tube. Cement which is present in said elongate opening due to cementing of the casing string in the borehole is drilled out first whereafter drilling of said one deviated borehole branch proceeds into the underground formation. Initiation of the other deviated borehole branch is performed in a similar way, whereby the drilling assembly is selectively oriented so that the drill bit is forced through the other elongate opening of the open-ended tube. Suitably a gyroscopic survey tool can be used in aid of orienting the drilling assembly in the selected orientation. Unwanted repositioning of the re-entry device due to movement of drilling or service tools through the borehole can be prevented by running a suitable hold-down tool on top of the re-entry device.

Claims: C L A I M S 1. Kick-off device in aid of drilling a pair of opposite deviated borehole branches in an underground formation from a single bore¬ hole comprising an open-ended tube provided at its upper end with connecting means to join the open-ended tube to a string of casing, and a guide element arranged in the open-ended tube near its lower end, which guide element includes two slanted guide ways arranged on opposite side--? of the guide element- 2. Kick-off device according to claim 1, wherein the slanted guide ways are hollow. 3. Kick-off device according to claim 1 or 2, wherein the wall of the open-ended tube has elongated openings facing the slanted guide ways. 4. Re-entry device which can be removably placed in the kick-off device according to anyone of the claims 1-3, comprising an open- ended liner having an elongated opening in its wall, a slanted deflecting surface arranged in the open-ended liner facing the elongated opening, wherein when the re-entry device can be so placed in the kick-off device that the slanted deflecting surface meets one of the two slanted guide ways. 5. Re-entry device according to claim 4, further comprising a meeting element arranged in the lower end part of the open-ended liner, which meeting element has a sole to allow the meeting element to rest on the guide element and includes a wedge-shaped part to allow placing the meeting element in a predetermined position with respect to one of the slanted guide ways.

Inventors: KONOPCZYNSKI MICHAEL ROBERT, KONOPCZYNSKI, MICHAEL, ROBERT
Applicants: SHELL CANADA LTD, SHELL INT RESEARCH, SHELL CANADA LIMITED, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1994
Main classification: E21B7
IPC codes: E21B7